The present invention relates to chemical analysis techniques, particularly to flow injection analysis systems, and more particularly to a miniaturized flow injection analysis system composed of a microflow system formed between bonded wafers, surface-mounted microvalves connected in the microflow system, and a detection cell.
The general concept of the chemical analysis technique known as flow injection analysis (FIA), involves small quantities of chemical reagents and a sample (liquid, gas, etc.) which are intermixed and reacted within a capillary flow system and the reaction products are detected optically, electrochemically, or by other means. An FIA system can consist of pumps (fluid or vacuum), valves, flow capillaries, flow separators, extractors, absorbers, and/or detectors. FIA systems provide inexpensive analysis of chemicals, foods, engine oil, environmental sensing, biological samples, etc., and thus have wide applications.
Silicon microfabrication technology developed for the semiconductor microelectronics industry is being increasingly applied to other scientific fields such as mechanical engineering, chemistry, biochemistry, and physics. Recent advances in micro-optics, micro-electro-mechanical systems (MEMS), and other microcomponents such as microflow channels, solid state optical and chemical detectors, thin membranes, analog and digital electronics, and recently microvalves, enable the development of revolutionary integrated microanalytical systems in much the same way that integrated circuits revolutionized the microelectronics industry.
One of the most promising new applications of MEMS in terms of performance and potential impact is development of analytical chemical microinstrumentation. The quantities and volumes required for chemical analyses and the forces required in analytical instrumentation are most compatible with the micron-scale of dimensions and forces encountered in MEMS. In addition, miniaturized instrumentation can be developed which will offer some unique advantages for applications involving in-situ analysis of trace quantities of substances. Micro-analytical instruments developed using integrated circuit-like microfabrication technology may have significant advantages in terms of performance, greatly reduced size, weight and costs--especially if wafer level fabrication techniques such as used to build integrated circuits can be adopted to allow automated and batch production of multiple micro-instruments on a wafer.
Four primary advantages exist for flow injection analysis. First the sensing system can be both sensitive and selective because the detector is optimized for sensitivity alone without regard to selectivity while the chemical reagents and flow system are optimized to yield high selectivity toward the contaminant of interest. For example hexavalent chromium has been detected at levels as low as 18 ppb with FIA. This is in contrast to most chemical sensors in which a difficult tradeoff exists between sensitive and selective detection. Second, analysis times are usually just a few minutes; the rapid throughput allows analysis of 2040 samples per hour. Third, the small size of the capillary minimizes the amount of reagents required and the volume of waste generated by the analytical procedure. Fourth, FIA is ideally suited for miniaturization-performance improves with reduced size. FIA is robust in the wide range of operating parameters under which one can achieve successful analyses; this allows the microdevice designer wide latitude in selecting among various trade-offs required during system development. Finally, recent advances in microfabricated valves, capillaries, microelectrodes, and optical sources and detectors allow development of miniature flow injection systems.
While recent efforts have been directed in miniaturization of FIA systems, the development of miniaturized FIA components has been successfully demonstrated, and the present invention provides integration of the components into a working system. The system of this invention comprises three (3) components; namely, a microflow system formed between bonded wafers or substrates, 2) surface-mounted microvalves, and 3) an optical absorption detection cell with fiber optics.